Modified colloidal silica and method for producing the same, and polishing agent using the same

Abstract

To provide modified colloidal silica capable of improving the stability of the polishing speed with time when used as abrasive grains in a polishing composition for polishing a polishing object that contains a material to which charged modified colloidal silica easily adheres, such as a SiN wafer, and to provide a method for producing the modified colloidal silica. Modified colloidal silica, being obtained by modifying raw colloidal silica, wherein the raw colloidal silica has a number distribution ratio of 10% or less of microparticles having a particle size of 40% or less relative to a volume average particle size based on Heywood diameter (equivalent circle diameter) as determined by image analysis using a scanning electron microscope.

The invention claimed is: 
     
       1. Modified colloidal silica comprising a residual oxidizing agent, being obtained by anion-modifying unmodified colloidal silica, wherein
 the unmodified colloidal silica has a number distribution ratio of 10% or less of microparticles having a particle size of 40% or less relative to a volume average particle size based on Heywood diameter (equivalent circle diameter) as determined by image analysis using a scanning electron microscope, and 
 wherein a residual oxidizing agent concentration in the modified colloidal silica is 1000 ppm by mass or less. 
 
     
     
       2. The modified colloidal silica according to  claim 1 , wherein the modified colloidal silica is modified with a sulfonic acid group. 
     
     
       3. Modified colloidal silica being anionically modified, comprising a residual oxidizing agent, wherein when a SiN wafer is subjected to an immersion treatment under a pH 2 condition and then washed with pure water, the number of particles having a particle size of less than 40% of a volume average particle size adhering to a surface of the SiN wafer is 50% or less relative to the number of particles having a particle size of 40% or more of a volume average particle size adhering similarly, and wherein a residual oxidizing agent concentration in the modified colloidal silica is 1000 ppm by mass or less. 
     
     
       4. The modified colloidal silica according to  claim 3 , wherein the total content of metal impurities is 1 ppm by mass or less. 
     
     
       5. A polishing agent, comprising the modified colloidal silica set forth in  claim 1 . 
     
     
       6. A polishing agent, comprising the modified colloidal silica set forth in  claim 2 . 
     
     
       7. A polishing agent, comprising the modified colloidal silica set forth in  claim 3 . 
     
     
       8. A polishing agent, comprising the modified colloidal silica set forth in  claim 4 .